50 years after I first encountered the following issue, but I finally figured out the cause!
Every time I had to install the cylinder barrel it was a struggle. The thing wouldn't align right so that it would simply lower into place. Always had to rock it this way and that and even after getting it down it never seated fully. The timing side rear always sat high.
So this afternoon I took a real close look at this. Set it in place with no studs present and measured the gaps with feeler gauge. Only the forward drive side made good contact. The timing side rear stud location had 11 thousandths gap!
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The question was what the hell was holding it up? No portion of the flange other than the forward drive side made contact at all. I could push down on the high side and it would sort of rock, the timing side went down and the drive side lifted.
Took the cases apart (there's nothing in them right now) and had a look setting them separately on the inverted barrel one at a time.
The timing side was first and by itself it sat down nicely. Little to no gaps.
The drive side however, even by itself resisted. Had to rock it around a bit to get it down. I noticed there was no play at all between a point over the cam location and the rear left of the cylinder bore skirt. The case half still rocked a little around these points, apparently it was enough of a bind to prevent the case half from dropping flat to the barrel.
There's scratch marks inside the case half where the skirt has been draging during installation.
Similarly the forward point also had scratch marks from contact with the cam follower bore skirt.
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I dressed up that front location some and now the barrel lowers on nicely onto the assembled cases and sits down flat without a struggle. Will need to recheck this with studs in place of course.
